BLUDICE

Hi, new on here - bought a '78 last Sunday and have a few things to fix. I have 1 head light door that does not want to go up, but will stay up once it is pulled up. Closes as it should when lights are turn off. I have just got into it and not started checking hoses or anything else. Any quick check advise would be helpful.
Thanks

Peterbuilt

Many times the seal (grommet) in the actuator goes bad, here how to troubleshoot and repair each part.
http://www.corvette-101.com/vacuum.htm

Easy Mike

Check the vacuum relay for that side. If the relay is good, you will need to check the actuator.

Mashman

With the car running, and the headlights on, pull the vacuum hose off the actuator on the engine side - that is the 'up' side. If you can feel vacuum on that hose, then the seal on the actuator has gone bad, if there is no vacuum on the hose, the the relay, is bad, or the hose from the relay to the actuator is loose.

Most likely issue is, as previously mentioned, the seal has gone. You can buy a new seal kit cheap, and it's easy to replace (once the actuator is out of the car). The actuator can be a bit of an issue, the easiest way is to remove the front grill, and pull it out that way.

BLUDICE

How many vacuum pounds is normal?

Mashman

Vacuum is measured in inches of Mercury (Hg). At idle, the engine should be producing around 15-20 inches HG. If the cam was replaced, then it's possible the engine is producing less vacuum.

The original post states that one headlight does come up, so I don't think inadequate vacuum is the issue.

If with the engine running, and the headlights on, you can feel vacuum on your finger, when it's pressed against the vacuum line going to the engine side of the actuator, then the problem is the actuator seal, and you need one of these - http://www.ecklerscorvette.com/corve...1968-1983.html

Since the headlight comes down when you turn off the headlights, then the relay is propperly diverting vacuum to the down side of the actuator, source is getting to the relay.

I would estimate it's about a 95% chance that it's the actuator seal. Not going up, but going down propperly is a very clear indicator.

BLUDICE

Is there a chance it could be the diapham or anything else - before I order the seal kit? Thanks very helpful info here.

Mashman

If the diaphram was leaking, then the headlight would not go down. The diaphram is in the middle of the actuator, and seals on the down side, the seals on the rod side seal for the up side.

If you want to make sure, then pull the actuator. My bet is that when it's out of the car, you will find that the atuator holds vacuum on the down side, but not on the up side.

You might be able to test this before removing it - i'm not sure. Disconnect the rod from the headlight door, and disconnect the vacuum hoses. Then while holding your finger over one of the vacuum ports, try moving the rod in and out.

My guess is that the rod will move fairly easily with your finger over the up side (bad seal), and not very easily when your finger is on the down side (good diaphram).

Dave J

You can do a quick check on the actuator rather easily. All this is with the engine off. To check the front seal, first raise the headlight manually. Then disconnect the vacuum hose from the rear, and plug the front vacuum port. Next release the pivot and slowly try to lower the headlight manually. If the front seal is good, it will prevent the headlight from closing. If it goes right down, the front seal is shot. If you have a vacuum gauge, you can hook it up to the front port, and observe the reading as you try to lower the headlight.